Method of treating photo-sensitive bodies



Patented Oct. 25, 1932 UNITED STATES PATENT OFFICE CARL ROEHRICH, OE BERLIN, GERMANY, ASSIGNOR TO THE FIRM SILFREE AKTIEN- GESELLSCHAFT, SILFREE LIMITED, 01 VADUZ, GERMANY METHOD OF TREATING PHOTO-SENSITIVE BODIES No Drawing. Application filed December 88, 1929, Serial No. 416,204, and in Germany April 88, 1929.

This invention is concerned with the prov duction of photographic films or plates and particularly with improvements over themethodsdisclosed in my copending applica- 5 tion, Serial No. 337,738, filed February 5,

The above mentioned original application has to do with an improved and simplified copying method, and those parts of this parent case, which are thou ht to be'essential for an understanding of t e present invention, will be verbally incorporated in the explanations and descriptions which are to .follow: --The usual procedure in producing films and the like consists in first making a negative in an well known manner and in then copying t is negative on a suitable transparent film, provided with a photosensitized layer.

This layer may be a silver-free colloid, sensitized by chromic acid salts. During the copying under the negative, the light rays striking the colloid layer will cause a hardening ofthe concerned sections to a certain depth. The quality of the film or plate depends largely on the uniformity-of the hardened sections or on the completeness of hardening. To explain this a little more in detail, it is essential that the hardening is uniform throughout the entire section and complete as to its thickness.

As has been said above, the copying under the negative produces partially hardened sections under ordinary conditions of exposure. Now, the further treatment of the films or plates may be performed in various ways, but it always produces difficulties on account of the incompleteness of the hardening. For example, dyes may be used for coloring the non-hardened arts. The coloring liquid is absorbed by t e non-hardened parts, and, since the adjoining hardened sections are only hardened to a certain depth, the coloring liquid may, similarly to the first case, enter underneath the hardened parts and produce dimmed pictures. On the other hand, if mordants are used for coloring the hardened sections, the results will'be undefined colors,

possibility of changin under the subsequent in uence of light rays.

be done in various ways and is because the hardened section is incomplete as long exposure or by storing in a moist atmosphere. However, these possibilities harbour serious difiiculties in view of the expense inci dent to their realization, e. g., the element of time introduced in both cases makes either case exceedingly costly. Furthermore the application of the above mentioned storage treatment in a moist atmosphere presents appreciable difiiculties incase of long films which can not be conveniently kept for any length of time. I v

The object of the invention disclosed in the copending application is to produce quality films or plates, and to overcome the handicaps of previous methods intimated above, in novel and more expedient ways,-particularly as explained below.

Up to the moment of copying the negative, the previously known methods and the' improvement disclosed in thercopending application run parallel. The difference appears in the manner in which uniformity and completeness are attained. While others.

have tried to reach this aim by the costly and time-consuming procedure of long exposure and storing in a moist atmosphere, the method proposed in the copending application aims to attain uniformityand completeness of hardening inexpensively and quickly.

After the first exposure, which produces hardened ,and unhardened sections on the film or plate, the unhardened sections are subjected to a treatment so as to prevent the their consistency This ma preferably effected by simple moistening in amoist atmosphere, by applying moisture by means of rollers, by spraying or washing, or in any other suita le manner. The film or platemay then be directly exposed to the action of light rays for a short period of time.

generally speaking, effects the sensitivity to The principles underlying the method dis-- closed above are as follows. Moistening,

light of the colloid layer. Since the nonhardened parts absorb moisture quickly, it is evident that the sensitivity of these parts :will

be greatly effected, while the hardened parts will remain relatively unaltered because of comparatively little absorption of moisture. Now, by re-exposing the colloid layer at this time to the direct action of light rays, the previously hardened parts having retained sensitivity, will again benefit by the exposure. Uniformity of hardening is thereby effected and completeness as to depth will be reached because the section, which at the time of the first exposure was only partially hardened, will now be hardened completely.

Referring to the difliculties experienced with previous methods, and particularly to the coloring of the films, as intimated previously, it' will be remembered that the coloring liquid might have entered underneath the partially hardened sections and thereby caused dim and faded pictures. The question is apparent, whether the moistening liquid too will. enter'underneath the partially hardened sections and produce reduction of light-sensitivity. If this condition should occur, there would be no advantage of the method explained over the known methods. It must be borne in mind, that the moisture, in order to reach the unhardened parts underneath the hardened parts, must penetrate the entire non-hardened adjoining sections and then enter the latter through tiny passages. Thorough investigations have revealed that no moisture enters in practice; therefore the question is merely of theoretic interest.

Another way of treating the plate prior to the second exposure consists in washing off the unhardened parts. This may be performed in anywell known manner, preferably in applying hot water to the film or plate, and thereby removing the unhardened parts.

It may be mentioned that during the washing off of the unhardened parts the hardened parts are l1xiviated by the applied water, losing their sensitization. They must therefore be re-sensitized before the plate is again exposed to light.

The last described method presents the disadvantage that the half-tones are spoiled.

0n the other hand the complete hardening ofthe hardened sections is efiected with certainty, which is particularly desirable, in

production of black-white pictures, e. g., such as used in trick-films, silhouette-films.

The second exposure may be made either directly on the colloid layer or from the other side through the carrier, provided that the carrier is transparent. It will be readily apparent that the result will be the same and in accordance with the description in the preceding paragraphs regardless from what side ing.

of the photosensitive body the second ex; posure is effected. Broadly summarizing the invention of the copending applicatiommentioned previously, the method disclosed therein consists in moistening the sensitive material after exposure and in then subjecting the same to a short reexposure without the use of a negative.

The present invention has for its object to further develop this method and to improve the same. The procedure explained above is based on the assumption that the parts hardened by the exposure do not absorb the moisture in the subsequent moistening process, while those parts which have not been struck by the light during the preceding exposure remained soft and absorb the moisture. Since the sensitivity of the colloid layer "is lowered by. the light rays and, accordingly, remained soft will be hardened only to a slight degree due to the absorbed moisture.

It was found that the moisture applied to the material exercises a slight, yet, noticeable detrimental influence also upon thesurface of the hardened parts. The detriment consists therein that the moisture enters into the hardened layer to a slight degree, thus reducing its sensitivity. A further lowering of the sensitivity is caused by the lixiviating influence upon the sensitizers due to the permeating moisture. i

The fact that the gradual drying of the surfaces of the hardened parts is apt to cause spots, might be listed as an additional disadvantage.

The instant invention preventsthe detriments enumerated above, by providing for quick removal of traces of moisture from the surfaces of the hardened parts. This is accomplished by adding to the moistening medium substances 7 having low evaporating point, e. g., an alcohol or ether. There are, of course, a great many other substances suitable for this purpose.

The quick drying of the traces of moisture upon the hardened parts may also be attained by first moistening the material in the usual manner and treating the same afterwards with a solution of low evaporating temperature, which treatment might consist of wash- There are, of course, numerous other ways for accomplishing the drying, e.-g., by the use of an air current which might even be heated suitably, or by the use of heat in other suitable manner-,or by mechanically drying the moisture residue, which latter manner may be realized by carrying the material over'drying barrels.

All these methods effect the removal of the moisture from those colloid layers on which the moisture should not exercise any influence. The subsequent re-exposure can, therefore, act upon the colloid parts which have been prehardened during the first exposure, without any detriment and handicap.

\Vhat is considered new over the disclosure contained in the copendingapplication, and desired to be protected by Letters Patent, is pointed out in the following claims.

What is claimed is:

1. Method of treating a photo-sensitive body having a colloid layerphoto-sensitized with an agent adapted to harden'the layer by reaction with light, consisting in exposing saidbody under a negative, thereby producing hardened and unhardened sections of said layer, in moistening said layerafter exposure, in removing the moisture from the' hardened sections of said layer,,and in thereafter re-exposing said body to light for a short period.

2. Method of treating a photo-sensitive body having a colloid layer photo-sensitized with an agent adapted to harden the layer by reaction with light, consisting in exposing said body under a negative, thereby producing hardened and unhardened sections upon said. layer, in moistening said layer after exposure to make said unhardened sections ineffective to the action of light rays, in remoying the moisture from the hardened sections of said layer, and in thereafter re-exposing said body to light for a short period.

3. Method of treating a photo-sensitive 355 body having a colloid layer photo-sensitized v with an agent adapted to harden the layer by 'reaction with light, consisting in exposing said body under a negative, thereby producing hardened and unhardened sections upon said colloid layer,-in moistening said layer after exposure to make said unhardened sec tions ineffective to the action of light rays, in thereafter treating said layer with a solution having low evaporating temperature to remove the moisture from-the surface of said hardened sections, and in thereafter re-exposing said body to light for a short period. c

4. Method of treating a photo-sensitive body having a colloid layer'photo-sensitized with an agent adapted to harden the layenby reaction with light, consisting in exposing saidbody under a negative, thereby producing hardened and unhardened sections upon. said colloid layer, in moistening said layer after exposure to make said unhardened sections ineffective to theaction of light rays, in removing the traces of moisture upon said hardened sections by the action of an air cur-' rent applied to said layer, and in thereafter re-exposing said body to light for a short period without the use of a negative.

5. Method of treating a photo-sensitive body having a colloidlayer photo-sensitized with an agent adapted to harden the layer by 65 reaction with light, consisting in exposing said body under a negative, thereby producing hardened and unhardened sections upon said colloid layer, in moistening said layer after exposure to make said unhardened sections ineffective to the action oflight rays, in mechanically removing the traces of moisture from said hardened sections by subjecting said body to the action of suitable drying devices, and in thereafter re-exposing said body to light for a short period without the use of a negative.

6. Method of treating a photo-sensitive body having a colloid layer photo-sensitized with an agent adapted to harden the layer by reaction with light, consisting .in exposing said body under a negative, thereby produc ing hardened and unhardened sections upon said colloid layer, in moistening said layer after exposure wit-h a medium containing a substance of low evaporating temperature to make said unhardened sections ineffective to v the action of light rays, whereby said substance of low evaporating temperature is added to said solution in order to effect quick drying of said hardened sections after the moistening process, and in thereafter re-exposing said body to light for a short period without the use of the negative.

7 Method of treating a photo-sensitive body having a colloid laye'i' photo-sensitized with an agent adapted to harden the layer by reaction with light, consisting in exposing said body under a negative, thereby producing hardened and unhardened sections upon said colloid layer, in moistening said layer after exposure to make said unhardened sections ineffective to the action of light rays, in thereafter chemically removing traces of moisturefrom the surfaces of said hardened sections, and in thereafter re-exposing said body .to light for a short period without the use of said negative.

8. Method of treating a photo-sensitive body having a, colloid layer photo-sensitized with an-agent adapted to harden the layer by reaction with light, consisting in exposing said body under a negative to produce hard ened and unhardened sections upon said colloid layer, in then moistening said layer after exposure to make said unhardened sections ineffective to the action of lightrays, 1n thereafter mechanically removin traces of moisture from the surfaces of said hardened sections, and in thereafter re-exposing said body to light for a short period.

In testimony whereof I afiix my signature.

CARL ROEHRICH. 

